Currently in San Francisco County 1 in 13 people has or has had Covid (but that's since 2020, so most of them are not currently contagious). About 1 in 1000 people in that county are being diagnosed with Covid per day, though, so it's serious . . . as it is in a bunch of other places right now.
The real thing to watch is how many people are getting sick compared to how much health care capacity a place has. Right now, NYC has about 1 person diagnosed with Covid per day for every 3 nurses. San Francisco has big teaching hospitals and a decent support net of other health care around it -- that's not equally true in a lot of rural counties that are facing higher rates of Covid per capita.